The present invention relates to coupling communication signals to electrical power distribution systems.
Communications signals can be coupled to electrical power distribution systems with various devices including broadband powerline modems. Many broadband powerline modems use spread spectrum modulation techniques, such as Orthogonal Frequency Division Multiplex (OFDM) or Direct Sequence Spread Spectrum (DSSS). For data rates of multi-megabits per second, such modems use a frequency band within the range of 1-50 MHz. One advantage of spread spectrum modulation is the ability to connect modems despite resonances and narrow band noise that may make certain segments of the frequency band unusable. But, it is still desirable to reduce the number of such unusable frequency segments and thereby increase the data rate and lower the error rate.
The signal output of a spread spectrum modem needs to be efficiently coupled to a power distribution line. Typically, this occurs at a point where such lines converge such as at the secondary terminals of a distribution transformer (DT) or a nearby junction point. However, the impedance at this coupling point, known as the drive point impedance, may vary widely from very low impedances over some frequency bands to very high impedances over other frequency bands. Relatively simple coupling techniques are likely to be reasonably efficient over some frequency bands, but may introduce significant coupling loss attenuation over other frequency bands.
Shunt coupling is one commonly used technique in which the modem is directly coupled across the power line by a series blocking capacitor. FIGS. 1A and 1B show shunt capacitive coupling of a modem to a power distribution system according to the prior art. The power distribution system includes a distribution transformer 135 with a secondary winding 130 having an impedance ZT 108. Modem A 110 provides a wideband high frequency current connected via a blocking capacitor 113 across power lines 115 and 117. Modem A 110 has an internal resistance RS 112.
In FIG. 1B, for frequency bands in which |ZT| less than  less than RS, ZT 108 heavily loads the output of Modem A 110 resulting in substantial coupling loss. Even if Modem A 110 had a low output impedance, it would suffer coupling attenuation when the impedance ZT 108 is much lower than a reflected load impedance ZLrefl (not shown). In such a case, most of the induced current from modem A 110 would flow through the lower magnitude ZT 108, and only a smaller portion would flow through ZLrefl towards Modem B 140. Thus, shunt capacitive coupling is inefficient for widely varying drive point impedances and for very low impedances.
Representative embodiments of the present invention include methods and corresponding systems for coupling a data signal over a power distribution system based on series inductance mode coupling with a shunt capacitor. An inductive signal coupler has two windings. The first winding is in series with a line conductor of the power distribution system. A capacitor is connected between the first line conductor and a second line conductor of the distribution system such that the capacitor presents a high impedance to a power signal and a low impedance to a data signal. A communication device is connected to the second winding so that a data signal can be coupled between the communication device and the distribution system.
In further embodiments, the line conductor may be a neutral conductor. The communication device may be a spread-spectrum modem. The inductive signal coupler may include a split magnetic core clamped over the line conductor, such that the second winding is wound over the core and a portion of the line conductor within the core acts as the first winding. The first winding may be adjacent to a secondary winding of the transformer within a distance equivalent to {fraction (1/10)} wavelength of a highest used frequency of the data signal. This positioning is close enough so as to put the coupler essentially at the terminals of the transformer""s secondary winding.
Representative embodiments of the present invention also include methods and corresponding systems for coupling a data signal over a power distribution system based on series inductance mode and parallel capacitance mode couplers. A series inductance coupler is connected to a first line conductor of a power distribution system. A shunt capacitive coupler is connected between the first line conductor and a second line conductor. A communication device has parallel first and second interfaces, the first interface being connected to one coupler and the second interface being connected to the other coupler, to enable coupling of a data signal between the communication device and the power distribution system.
In further embodiments, the line conductor may be a neutral conductor. The communication device may be a spread-spectrum modem. The inductive signal coupler may include a split magnetic core clamped over the line conductor, such that the second winding is wound over the core and a portion of the line conductor within the core acts as the first winding. The first winding may be adjacent to a secondary winding of the transformer, i.e., within {fraction (1/10)} wavelength of a highest used frequency of the data signal.
Representative embodiments of the present invention also include methods and corresponding systems for coupling a data signal across a low impedance node of a power distribution system. A capacitor is connected in parallel with a low impedance node of a power distribution system, and presents a high impedance to a power signal and a low impedance to a data signal. A first inductive coupler is connected in series with a line conductor, upstream of the node. A second inductive coupler is connected in series with the line conductor, downstream of the node. The first inductive coupler and the second inductive coupler are operably connected to couple the data signal across the node.
In a further embodiment, a signal amplifier operably connects the first inductive coupler and the second inductive coupler. Alternatively or in addition, a data router may operably connect the first inductive coupler and the second inductive coupler to selectively route a data signal between the first inductive coupler and the second inductive coupler. In that case, the second inductive coupler may be one of a plurality of inductive couplers downstream of the node, so that the data router selectively routes data signals between the first inductive coupler and the plurality of inductive couplers.